Hi Roger,
It's a mix of alot of things I read about. It's a 35 shoulder like the WSM, has a 300 Rum body taper, the neck length came from a formula I found that theorizes why 6 PPC's and 300 WSM's are accurate. The water capacity slightly over an improved 300 Wby and the throat to set a 240 at the neck junction. Although there are no worries of a doughnut here because it has to get reamed out before you can seat a bullet.
338 straight taper neck, loaded round 335.
I used a RCBS 338 Lapua die with the base ground off for the first pass, a RCBS 30-378 die with the base ground off for the next pass (had to slightly hone the base of the die), cut off the neck with a homemade dremel tool table saw, honed down the Forester trimmer pilot to accept the fat necks and trimmed, annealed, fireformed with 20gr unique and cream of wheat, reamed with a custom Forster .309 reamer,and outside turned. My gunsmith ran the reamer in a set of Redding competition seater and neck size die inserts (formerly 300 Wby). Ran the reamer into a Wilson 338 Lapua case holder and finish trimmed the brass.
I do lack a full length / body die, once I get three cases fired 3 times, I am going to contact Neil Jones for that.
When I eventually get the Hornady dies, I am going to set them on the shelf with a big sign that says, "Although these were the price of two barrels, smile, there was a valuable lesson learned here.". They do make danged good bullets though.
The action is a Weatherby Mark V.
Shummy